1. Field of the Invention
This invention relates generally to log structures and, in particular, to load-bearing columns within log walls for supporting logs, joists, rafters, purlins, columns, and ridges bearing upon log walls.
2. Description of the Related Art
It is known that wooden logs shrink over time, due to the loss of water. Logs generally shrink more in their width than in their length. The amount, rate, and duration of shrinkage depend upon the level of humidity in the environment. Overall, logs shrink more in dry weather than they do in humid weather. This is because, in dry weather, the logs lose more of their water before reaching an equilibrium point with the environment. Logs also shrink faster in dry weather than in humid weather. In a drier environment, for example, a log having a diameter of about 8-15 inches can shrink as much as 3/4 of an inch in one year. The shrinkage rate tends to be greater in the first year and generally tapers down thereafter. Conversely, the duration of log shrinkage is generally greater in more humid environments. Logs typically shrink for a duration of about somewhat less than a year to as long as four years.
Log shrinkage causes a variety of problems in log buildings, such as log homes. Typically, these buildings have walls that comprise stacks of horizontal wooden logs ("log wall stacks"). Over time, the logs in log wall stacks tend to move downward, due to the shrinkage of all of the logs. For example, if each of the logs in a 12 log wall shrinks one inch in width, then the height of the entire wall will decrease by one foot. Each log will move downward a distance equal to the total shrinkage of each of the logs below. Such downward motion can cause damage to internal structures within the walls, such as doors and windows. Often, doors and windows collapse under the weight of downward moving logs above.
For example, a log wall stack may contain a window frame enclosing a glass window. The window frame may comprise a vertical log on each side of the window. The window and frame will not shrink much at all in height over time. As the wall moves downward, due to shrinkage, the log directly above the window frame begins to bear against the frame. As the horizontal logs on each side of the window frame shrink further, the window and frame are compressed due to the weight of the logs above. Such weight can cause the frame and window to collapse.
Methods employed to deal with this problem are burdensome, inconvenient, and expensive. One approach has been to build log homes with wall cavities provided directly above structures within the log walls, such as doors and windows. As the logs shrink over time, the logs above can gradually move downward and occupy such cavities without damaging the internal wall structures. However, this may only delay the damage, since the logs might eventually move downward sufficiently to bear against the internal structures anyway. Also, the delay can be increased only by increasing the height of the wall cavities above the internal structures, which reduces the building integrity. Further, the wall cavities are normally covered with some type of panel or facade, which may be aesthetically displeasing.
Another problem caused by the downward movement of horizontal logs is that it upsets the positional relationship between the horizontal logs and the vertical logs in the wall. Vertical logs are commonly used to build the frame of the house. Vertical logs often serve as columns to support the roof of the building and to transfer the weight of the roof to a fixed base. Also, internal wall structures often include vertical logs. For instance, a door frame or window frame may include vertical logs on its sides. Since wooden logs do not shrink significantly in their lengthwise direction, the vertical logs do not decrease much in height. Thus, log shrinkage upsets the positional relationship between horizontal and wooden logs.
A known method of dealing with this problem is to provide a short threaded rod, known as a screw jack, at the bottom end of each of the vertical logs. The threaded rod is fixed with respect to the foundation of the building. The vertical log has a short vertical channel which slidably receives the threaded rod so that the log can be slightly raised or lowered while maintaining a sliding engagement between the log and the threaded rod. The log rests upon a nut threadingly engaged with the rod. The nut bears the weight of the log as well as part of the weight of the rest of the building. The nut can be rotated so that the nut and log move vertically along the threaded rod. In this manner, the vertical log can be raised or lowered, relative to the fixed foundation of the building. Over time, as the horizontal logs descend due to log shrinkage, upsetting the positional relationship between the horizontal and vertical logs, the vertical logs are lowered to compensate for the downward movement of the horizontal logs.
Unfortunately, this method is very difficult, time-consuming, and expensive. The amount of downward displacement of the horizontal logs can vary throughout the structure, and must be measured throughout the walls. Thus, each of the vertical logs may have to be lowered by different amounts, complicating the procedure. Also, the procedure, i.e., the lowering of the vertical columns, must be repeated periodically. It is normally repeated once or twice a year. This further increases the cost and time consumption of this method. Further, the lowering of vertical logs can cause the roof to become uneven, which reduces the building integrity.
The above-described methods of dealing with the problems associated with log shrinkage merely compensate for or prevent damage that may result from the downward movement of logs in a log wall stack. Thus, there is a need for a method of preventing the downward movement of logs due to log shrinkage.